The present invention relates to driving arrangements in general, and more particularly to a driving arrangement for a pump, especially for a liquid metering pump.
There are already known various constructions of driving arrangements of the type here under consideration, among them such which include a motor-driven pump tappet which is displaceable in and opposite to a predetermined direction during a pumping and a return stroke, respectively. Known liquid metering pumps driven by an electric motor powered drive of this type typically include a step-down transmission which drives an eccentric or cam disc which, in turn, acts on the pump tappet. The return stroke is then performed under the influence of a restoring spring. There may further be provided a stroke limiter which is positionally adjustable from the exterior of the driving arrangement. This principle is usable with piston pumps as well as diaphragm pumps. In these known constructions, the output power of the motor is used only for the displacement of the pump tappet in the predetermined or pumping direction. During the return or suction stroke, the motor operates in an idle mode. During the course of the pumping stroke, the motor causes the force which is exerted on the pump tappet in the predetermined direction to gradually and steadily increase from a relatively low level up to a maximum or peak level achieved when the eccentric member has displaced the pump tappet to the largest possible extent during the pumping stroke. Therefore, the driving motor must be dimensioned so as to have an output power sufficient to sustain the peak load. However, in the known liquid metering pumps, the satisfaction of this requirement means that, during most of the stroke cycle, and especially during the return stroke, the output power of the motor is unused so that, on the average, it is necessary to overdimension the motor.